Can this be pregnancy or just my head playing wit me??? (dont b rude)?

I ususally get sings a week or 2 before my period actually comes and i havent for this month, i kow after my period i had everynight for the past 18 days maybe out of them days we didnt 2 or 3 days. we started on the exact day i finished my period wich was feb 21,2008. My period started on Feb 17, 2008.. My cycle i think is 28 or 30.. I have been feelig very very lite cramping, bloating and gasy but other then that nothing, usually i get the normal symptoms of your menstrual period, What do u thik can this be my period is due tomorrow you think it can be pregnancy or just my head playing games wit me..?? Also me and my olda sis got our periods last month on feb 17 and this month she got it on feb11 or 12, should i had gotten it the same day as her or no?? not sure how long is her cycle..